Pneumatic tires are constructed out of a number of different rubber and metal components. In conventional tire construction, the rubber parts are often in sheet form and are wound or placed around the tire building drums after being cut and then spliced to form a continuous tubular or annular structure around the drum. In other words, the sheet component, after being bias cut, is usually wrapped around the drum and the overlapping ends of the sheet joined to produce axially extending seams. Such seams are generally undesirable in that they produce a discontinuity in the annular construction which results in weak spots which are more susceptible to failure than other parts of the tire. Leakage at poorly bonded seams can allow moisture and reactive gases (such as oxygen) into the tire which can lead to corrosion of the steel reinforcing filaments and separation of the tire plies. Ultimately such deterioration will result in failure of the tire. The seams inherent in conventional tire construction may produce bumps or undulations in the sidewall surface. These imperfections are thought by some to be objectionable for aesthetic or marketing reasons. At the same time, the presence of such seams inherently results in structural asymmetry in the finished tire which manifests itself as variations of radial and lateral forces and other non-uniform parameters. Such variations need to be minimized to meet current automobile maufacturer specifications. In the extreme, the imbalance induced by structural asymmetry of a spliced tire can cause premature tire failure under severe service conditions. Modern, efficient high speed methods of tire curing favor bladderless curing. The absence of bladders in bladderless curing exposes the tire interior to the expanding medium (usually air, steam or nitrogen) which may infiltrate the tire's structure through seams and weaken its structure. At the same time, in bladderless curing the seams are not flattened or soothed out. Their appearance has been found by some to be objectionable from aesthetic or marketing aspect. The coextruded, seamless tire bodies of the present invention obviate these problems and permit bladderless curing without incurring these detriments.
Still further, the coextruded tubular spliceless tire body manufacturing techniques of this invention reduce the need for manufacture and assembly of individual tire structural components such as tire body plies, air sealing innerliners, sidewalls, reinforcing strips and other various components. This is because the process of this invention allows several conventional tire components to be simultaneously made and incorporated into a tubular composite structure. Thus tires made by conventional hand assembly techniques can be more costly and less uniform than those made by the practice of this invention using coextruded seamless tubular tire bodies.
It is an object of the present invention to reduce or substantially eliminate many, if not all of the aforementioned difficulties and problems in conventional tire manufacture and assembly methods.
It is also an object of this invention to provide coextruded tire bodies embodying in a single structural composite several conventional tire structural components. Other objects will become apparent from study of this specification and the accompanying claims.